A HEIC was being decoded once per rung. av-club is stateless per request, so
seven rungs asked for from the original are seven ImageMagick conversions of it
— measured on fofos at 8.5 s each, against 1.1 s for the resize and encode that
follow. Six of the seven produced a pixel-identical intermediate and threw it
away: about 67 seconds per photograph where 16 would do, paid again on every
future upload.
So when av-club says a format needs converting, convert it ONCE into the staging
directory and cut every rung from that. `needsConversion` is asked rather than
guessed, because which formats are expensive is av-club's fact and a list of
them kept here would go on paying after its build stopped needing it. JPEG and
PNG are untouched — writing a full-resolution intermediate to save six cheap
reads would cost more than it saved.
Concurrency drops to one. Two was chosen to match av-club and is the right
number on a machine with room; fofos has 1.87 GiB of RAM, and two concurrent
12-megapixel decodes left 520 MiB free with 648 MB already paged out. The work
is CPU-bound on a box already at 99%, so the second worker was not buying
throughput — it was buying a second resident bitmap.
And the sharp calls now name their output format properly. `output` takes
`{ format, options }`; passing `{ webp: { … } }` was silently ignored, so
everything built before this encoded at sharp's default quality rather than the
82 asked for.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
pastilhasandClaude Opus 5
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